You Are Not a Small Man: What Every Woman Should Know About Intermittent Fasting
If you’ve ever tried intermittent fasting and thought, “Why does this work for everyone but me?”—you’re not crazy. You’re just a woman with a cyclical body. And most of the research hyping up the benefits of fasting? It’s done on men.
Men, with their consistent 24-hour hormonal rhythm, respond to fasting in predictable ways. But women—especially those of us still cycling—are working with a completely different system. One that changes week to week. One that was never designed to thrive on chronic stress, skipped meals, or nutrient deprivation.
So before you beat yourself up for not crushing 16:8 fasting windows like your favorite podcaster, let’s talk about what’s really going on—and why your hormones deserve a seat at the table.
The Research Is Built on Men (and Postmenopausal Women)
Most of the big claims around fasting—fat loss, insulin sensitivity, improved cognition—come from studies done on men or postmenopausal women. Why? Because premenopausal women have what researchers consider “too many variables.” AKA: hormones.
This matters. Because women’s cycles impact everything: cortisol, insulin sensitivity, appetite, metabolism, and even how we emotionally respond to stress. As Dr. Stacy Sims says: “Women are not small men.”
And yet, most fasting advice doesn’t even mention this.
Your Cycle Changes Everything
Let’s break it down. Your cycle isn’t just about bleeding. It’s a full hormonal arc that impacts how your body functions each week:
Follicular Phase (Day 1–Ovulation): Estrogen is rising. You’re typically more insulin sensitive, stress-resilient, and metabolically flexible. Fasting may feel easier here.
Ovulation: Energy, libido, and confidence peak. Your body is primed for connection and creativity. Still relatively metabolically strong.
Luteal Phase (Post-Ovulation): Progesterone dominates. You become less insulin sensitive, your metabolism speeds up, and your body is biologically prepping for a potential pregnancy. Your cortisol threshold is lower, and fasting can feel like a straight-up assault.
Menstrual Phase: Hormones drop. Energy is low. This can be a time to rest and nourish, not restrict.
If you’ve ever felt like you’re “failing” at fasting one week, then thriving the next—it’s not a mindset issue. It’s your hormones doing exactly what they’re meant to do.
The Luteal Phase: Where Fasting Backfires
This is the phase no one warns you about. When progesterone is high, your body becomes naturally more insulin resistant. That’s normal. Your metabolism also increases slightly, which is why you’re hungrier in the days before your period.
If you try to push through with long fasts during this phase, you’re more likely to:
Spike cortisol
Crash your blood sugar
Trigger anxiety or insomnia
Worsen PMS
Suppress ovulation in the next cycle
This is your body waving a red flag—not because it’s broken, but because it’s smart. It’s trying to protect your fertility.
So When Can Women Fast?
If you want to experiment with fasting, your best window is the follicular phase. That’s when estrogen is doing her magic, making you more insulin sensitive and resilient to stress. Even then, it’s best to keep your fasts gentle: 12–14 hours max, and definitely not daily.
And during the luteal phase? Prioritize blood sugar stability. Eat breakfast. Don’t skip meals. Focus on protein, fat, and fiber. This isn’t the time to push—it’s the time to support. Dr. Stacy Sims calls this “feeding the physiology,” not fighting it.
Listen to Your Cycle, Not the Algorithm
You don’t need to force yourself into a fasting protocol designed for a male body. You need to track your cycle, understand your patterns, and work with your biology—not against it.
If you’re feeling burned out, bloated, anxious, or like fasting just “isn’t working” for you—it might be your body asking for food. And you should probably listen!